The present invention relates generally to hydraulic mining tools utilized for the recovery of subterranean mineral deposits and more particularly to an improved hydraulic mining tool and method of hydraulically mining unconsolidated mineral formations, such as tar sands and the like.
Hydraulic mining apparatus is well-known in the art, being characterized by the use of a high velocity liquid stream being discharged directly into a subterranean mineral deposit. The liquid stream dislodges minerals from the subterranean mineral bed and forms a resultant mineral slurry which may be subsequently pumped upward through the interior of the mining tool to ground surface. Examples of various hydraulic mining tools are disclosed in the U.S. Pat. No. 3,951,457 issued to Redford, and my co-pending application Ser. No. 053,029, filed June 28, 1979, now the U.S. Pat. No. 4,275,926, entitled Downhole Pump With Bottom Receptor, the disclosures of which are expressly incorporated herein by reference.
The vast majority of such hydraulic mining tool apparatus have been utilized to recover minerals such as uranium, coal and/or potash, which typically are sufficiently consolidated in their natural formation state such that as mined material is removed from the subjacent portions of the mineral bed, the mineral bed, and in particular the overburden located above the mineral bed, is continuously supported during the mining process. Thus, in the hydraulic mining of such consolidated formations, substantial quantities of the mineral bed may be removed from the formation, without experiencing any significant downward migration of the overburden into the mineral bed or an attendant ground surface subsidence. However, in the hydraulic mining of unconsolidated mineral formations such as tar sands and the like, unique overburden support problems exist, which to a great extent has rendered the majority of existing hydraulic mining tools and their methods of operation unsuitable and commercially infeasible.
In contra-distinction to consolidated mineral formations, unconsolidated mineral formations generally are non-uniform in composition and typically possess relatively small magnitude cementation forces between individual mineral particles, whereby the unconsolidated formations fail to possess the necessary degree of stabilization to support the overburden during the hydraulic mining process. Thus, as the subjacent portions of the unconsolidated mineral bed are removed during the mining process, the overburden often compacts and migrates downward into the mineral bed wherein it mixes with the mined mineral slurry and is subsequently transported upward to ground surface. The mining of such non-mineral bearing overburden reduces the overall efficiency of the hydraulic mining process, and if substantial, may reduce the economic effectiveness of the process below acceptable profit levels. Further, in those instances where this downward migration of the overburden becomes acute, a general subsidence of the overburden may be experienced which may result in a bending or "twist-off" of the mining tool within the mineral bed.
In addition, due to the small magnitude cementation forces existing in mineral formations, the amount of mineral particles freed from the mineral bed during the mining process often is extremely large and may exceed the saturation or suspension level of the discharged liquid within the mineral bed. When this saturation condition occurs, the freed mineral particles fail to be carried or suspended for sufficient period of time within the slurry and typically migrate downward to the lowermost portion of the hydraulic mining cavity. Since the transport to ground surface of the mined material during the hydraulic mining process is dependent upon the existance of a slurry condition, any freed mineral particles falling to the lowermost portion of the mining cavity have heretofore remained in the cavity and been unrecoverable. Thus, the efficiency of the prior art hydraulic mining processes have been significantly low in the the recovery of unconsolidated mineral formations.
Hence, there exists a substantial need in the art for an improved apparatus and method of hydraulically mining unconsolidated mineral formations which reduces the susceptibility of subsidence of the overburden during the mining process, minimizes the possibility of damage to the mining tool upon experiencing a subsidence of the overburden, and further, increases the suspension of mined material within the slurry during the mining process.